1. Field of Invention
This invention relates to a document dependent maintenance procedure for ink jet printers, and more particularly to a maintenance procedure utilized in ink jet printers to maintain proper operation of the printhead. In embodiments, the present invention relates to maintenance procedures where printhead maintenance intervals are determined based upon the type of documents being printed. The present invention also relates to control structures for implementing such maintenance procedures, and printers incorporating such maintenance procedures and control structures.
2. Description of Related Art
Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based or thermal, have at least one printhead from which droplets of ink are directed towards a recording sheet. Within the printhead, the ink is contained in a plurality of channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the end of the channels.
In a thermal ink-jet printer, the power pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated channel and initially bulges from the channel orifice followed by collapse of the bubble. The ink within the channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a dot or spot of ink is deposited. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink. Operation of a thermal ink-jet printer is described in, for example, U.S. Pat. No. 4,849,774.
The ink jet printhead may be incorporated into either a carriage type printer, a partial width array type printer, or a page-width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage, which is reciprocated to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. This procedure is repeated until the entire page is printed. In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width or length of a sheet of recording medium at a time. The recording medium is continually moved past the page width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an ink jet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods of time. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the orifices. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. Nos. 4,855,764, 4,853,717, and 4,746,938. Removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
It has been found that to properly maintain an ink jet printhead, two separate operations must be performed. In a first operation, a maintenance assembly is typically used to maintain proper condition or operation of the printhead nozzles by priming the nozzles, by wiping clean the nozzle face of the printhead, and/or by vacuuming the face of the printhead to remove any contaminants or ink that may have collected thereon. The second operation is to cap the printhead if the printhead nozzles will be exposed to air for extended periods of time to thereby prevent the ink contained in the nozzles from drying out. To prevent drying, a cap is brought into contact with a printhead to form a substantially airtight seal with the face of the printhead and around the nozzles.
Various methods and apparatus for maintaining the condition of ink jet printheads are generally known in the art, as illustrated and described in the following references.
U.S. Pat. No. 4,908,638 to Albosta et al., describes an n-way selecting mechanism for selecting inks from a number of ink supply containers for delivery to the marking head (printhead) of an ink jet printer. The selecting mechanism includes a rotary diverting valve, which is positioned to allow the marking head to receive ink from one color supply container or another supply container.
U.S. Pat. No. 3,586,049 to Adamson describes an oscillatory valve for selectively connecting three inlets to an outlet.
U.S. Pat. No. 5,206,666 to Watanabe et al., describes an ink jet recording apparatus having a full-line type recording head rotatably supported between a recording position and a non-recording position. A cleaning member contacts the recording head during rotation of the recording head to remove deposited ink or foreign matter. In the non-recording position, the printhead is capped.
U.S. Pat. No. 5,257,044 to Carlotta et al., describes a cap actuation mechanism for use in a maintenance station for an ink jet printhead in a scanning type ink jet printer. A cap located on a cap carriage in an ink jet printer maintenance station provides the functions of printhead nozzle capping, priming, cleaning, and refreshing, as well as waste ink management.
U.S. Pat. No. 5,367,326 to Pond et al., describes a pagewidth ink jet printer having a movable cleaning/priming station adapted for movement parallel to and along an array of printhead nozzles. The cleaning and priming station is slidingly moved along a ledge surface so that the cleaning and priming station is maintained a fixed distance from the face of the printhead.
As apparent from the above references, a printhead maintenance assembly generally comprises multiple components, used for maintaining and/or capping the printhead. For example, a typical maintenance assembly may include: (1) a cap assembly that can be moved to seal around the exterior of the printhead nozzle surface while staying as far away from the nozzles as possible so as to provide an environment in which drying air is excluded while the nozzles are capped; (2) a wiper that can be raised to engage the nozzle surface of the printhead and clear away ink, debris and undesirable matter collected on the surface of the nozzle plate area, and lowered when wiping is not desired; (3) a "spit cup" for receiving ink ejected from the nozzles to remove contaminated ink from the nozzles and maintain less used nozzles in proper working order; (4) a selectively energizable drive assembly including a gear train for moving the cap, wiper and spit cup; and (5) an absorption pad for maintaining liquid ink so that the printer may be transported without damaging or soiling parts of the printer with purged ink.
However, the maintenance assemblies are complicated by the increasing use of colored inks (i.e., multiple colors other than or in addition to black ink) in the ink jet printers. For example, water resistant monochrome ink typically requires little spitting maintenance but requires a significant wiping force to be exerted to wipe the fast drying ink from the nozzle plate area. On the other hand, a tri-color printhead with its smaller nozzles and slower drying ink requires many more spits and wipes, but because the wiping is more frequent and the ink is slower drying, a lighter wiping force can be used and is preferred. Also, a tri-color printhead poses the problem of wiping the ink and debris from the nozzle surface without transferring ink of one color to the area of the nozzles that eject ink of another color. Thus, in order for a single printhead maintenance system to operate satisfactorily during color and monochrome printing, it must be capable of responding to the different needs of the printhead geometry presented to it. Furthermore, the maintenance assemblies are more complicated based on whether the printer is used to print one color ink or multiple color inks, and whether the multiple color inks are contained in a single printhead or in multiple printheads. For example, in existing printhead maintenance mechanisms used in ink-jet printers, either each color of the printhead can have a separate maintenance assembly or, if all of the colors are housed in one printhead and the monochrome (usually black) is housed in another printhead, the two separate printheads may each have a separate maintenance assembly. This is generally true regardless of whether the color printhead and the black printhead reside in the printer at the same time or if the two printheads are interchangeably mounted on a single printhead carrier.
A problem with the various known ink jet printhead maintenance systems and procedures, however, is that the maintenance procedures by their nature decrease printer throughput. That is, because time must be taken to perform the maintenance procedure, printing must be halted, or the start of printing must be delayed, so as to allow the maintenance procedure time to complete its functions. Furthermore, printer productivity is decreased due to the expenditure of ink in the operation. For example, when the maintenance procedure requires ejecting ink from the printhead into a catch basin, that ink can not be used for subsequent printing, and is lost. As the number or frequency of maintenance periods increases, the amount of printing that can be performed with a given volume of ink accordingly decreases.